It is well known that high molecular weight aromatic polycarbonate resins have excellent impact strength below a critical thickness of about 0.20 inch. Above this critical thickness the impact strength of these polycarbonate resins drops precipitously. Various impact modifiers are known to dramatically increase the "thick section", 1/4 inch, impact of these polycarbonates. Some of these impact modifiers include polyolefins, U.S. Pat. No. 3,431,224 butadiene containing polymers, U.S. Pat. No. 3,880,783 and acrylate containing polymers, U.S. Pat. No. 4,299,928. However even with these impact modifiers present in the polycarbonate composition, the low temperature impact strength of the composition still reflects the polycarbonate tendency to lose impact strength and become embrittled as temperature decreases, particularly below 5.degree. C.
A series of ternary compositions including polycarbonate has recently been patented which shows increased impact strength at low temperatures as well as normal temperatures. These compositions all have polycarbonate, an acrylate methacrylate copolymer particularly of the "core-shell" type and a third component which significantly increases the thin section impact strength at low temperatures. Examples of third components which accomplish this are olefin-acrylates, U.S. Pat. No. 4,260,693; polyolefins, U.S. Pat. No. 4,245,058, silicone oils, U.S. Pat. No. 4,263,416; polyethylene oxide, U.S. Pat. No. 4,340,683; and polyester, U.S. Pat. No. 4,320,212. However, ease of processability, is generally not mentioned.
Various alkanes and paraffin waxes have been used as lubricants for aromatic polycarbonate. However, accompanying the lubricating qualities is a significant decrease in the composition's impact strength as well as embrittlement in comparison to the polycarbonate per se.
It has now been discovered that when aliphatic hydrocarbons are in admixture with polycarbonate and an acrylate impact modifier, the thick section impact and ductility of the binary composition at normal temperature is essentially maintained while the thin section (1/8 inch) impact and ductility of the binary composition at reduced temperatures is substantially improved. In addition the new composition is easier to process as shown by substantially reduced melt viscosity by melt flow Index.